/*H:420
* This is the routine which actually sets the page table entry for then
* "idx"'th shadow page table.
*
* Normally, we can just throw out the old entry and replace it with 0: if they
* use it demand_page() will put the new entry in. We need to do this anyway:
* The Guest expects _PAGE_ACCESSED to be set on its PTE the first time a page
* is read from, and _PAGE_DIRTY when it's written to.
*
* But Avi Kivity pointed out that most Operating Systems (Linux included) set
* these bits on PTEs immediately anyway. This is done to save the CPU from
* having to update them, but it helps us the same way: if they set
* _PAGE_ACCESSED then we can put a read-only PTE entry in immediately, and if
* they set _PAGE_DIRTY then we can put a writable PTE entry in immediately.
*/
static void __guest_set_pte(struct lg_cpu *cpu, int idx,
unsigned long vaddr, pte_t gpte)
{
/* Look up the matching shadow page directory entry. */
pgd_t *spgd = spgd_addr(cpu, idx, vaddr);
#ifdef CONFIG_X86_PAE
pmd_t *spmd;
#endif
/* If the top level isn't present, there's no entry to update. */
if (pgd_flags(*spgd) & _PAGE_PRESENT) {
#ifdef CONFIG_X86_PAE
spmd = spmd_addr(cpu, *spgd, vaddr);
if (pmd_flags(*spmd) & _PAGE_PRESENT) {
#endif
/* Otherwise, start by releasing the existing entry. */
pte_t *spte = spte_addr(cpu, *spgd, vaddr);
release_pte(*spte);
/*
* If they're setting this entry as dirty or accessed,
* we might as well put that entry they've given us in
* now. This shaves 10% off a copy-on-write
* micro-benchmark.
*/
if ((pte_flags(gpte) & (_PAGE_DIRTY | _PAGE_ACCESSED))
&& !gpte_in_iomem(cpu, gpte)) {
if (!check_gpte(cpu, gpte))
return;
set_pte(spte,
gpte_to_spte(cpu, gpte,
pte_flags(gpte) & _PAGE_DIRTY));
} else {
/*
* Otherwise kill it and we can demand_page()
* it in later.
*/
set_pte(spte, __pte(0));
}
#ifdef CONFIG_X86_PAE
}
#endif
}
}
/*H:330
* (i) Looking up a page table entry when the Guest faults.
*
* We saw this call in run_guest(): when we see a page fault in the Guest, we
* come here. That's because we only set up the shadow page tables lazily as
* they're needed, so we get page faults all the time and quietly fix them up
* and return to the Guest without it knowing.
*
* If we fixed up the fault (ie. we mapped the address), this routine returns
* true. Otherwise, it was a real fault and we need to tell the Guest.
*/
bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
{
pgd_t gpgd;
pgd_t *spgd;
unsigned long gpte_ptr;
pte_t gpte;
pte_t *spte;
/* Mid level for PAE. */
#ifdef CONFIG_X86_PAE
pmd_t *spmd;
pmd_t gpmd;
#endif
/* First step: get the top-level Guest page table entry. */
if (unlikely(cpu->linear_pages)) {
/* Faking up a linear mapping. */
gpgd = __pgd(CHECK_GPGD_MASK);
} else {
gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
/* Toplevel not present? We can't map it in. */
if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
return false;
}
/* Now look at the matching shadow entry. */
spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) {
/* No shadow entry: allocate a new shadow PTE page. */
unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
/*
* This is not really the Guest's fault, but killing it is
* simple for this corner case.
*/
if (!ptepage) {
kill_guest(cpu, "out of memory allocating pte page");
return false;
}
/* We check that the Guest pgd is OK. */
check_gpgd(cpu, gpgd);
/*
* And we copy the flags to the shadow PGD entry. The page
* number in the shadow PGD is the page we just allocated.
*/
set_pgd(spgd, __pgd(__pa(ptepage) | pgd_flags(gpgd)));
}
#ifdef CONFIG_X86_PAE
if (unlikely(cpu->linear_pages)) {
/* Faking up a linear mapping. */
gpmd = __pmd(_PAGE_TABLE);
} else {
gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
/* Middle level not present? We can't map it in. */
if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
return false;
}
/* Now look at the matching shadow entry. */
spmd = spmd_addr(cpu, *spgd, vaddr);
if (!(pmd_flags(*spmd) & _PAGE_PRESENT)) {
/* No shadow entry: allocate a new shadow PTE page. */
unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
/*
* This is not really the Guest's fault, but killing it is
* simple for this corner case.
*/
if (!ptepage) {
kill_guest(cpu, "out of memory allocating pte page");
return false;
}
/* We check that the Guest pmd is OK. */
check_gpmd(cpu, gpmd);
/*
* And we copy the flags to the shadow PMD entry. The page
* number in the shadow PMD is the page we just allocated.
*/
set_pmd(spmd, __pmd(__pa(ptepage) | pmd_flags(gpmd)));
}
/*
* OK, now we look at the lower level in the Guest page table: keep its
* address, because we might update it later.
*/
gpte_ptr = gpte_addr(cpu, gpmd, vaddr);
#else
/*
* OK, now we look at the lower level in the Guest page table: keep its
* address, because we might update it later.
*/
gpte_ptr = gpte_addr(cpu, gpgd, vaddr);
#endif
if (unlikely(cpu->linear_pages)) {
/* Linear? Make up a PTE which points to same page. */
gpte = __pte((vaddr & PAGE_MASK) | _PAGE_RW | _PAGE_PRESENT);
} else {
/* Read the actual PTE value. */
gpte = lgread(cpu, gpte_ptr, pte_t);
}
/* If this page isn't in the Guest page tables, we can't page it in. */
if (!(pte_flags(gpte) & _PAGE_PRESENT))
return false;
/*
* Check they're not trying to write to a page the Guest wants
* read-only (bit 2 of errcode == write).
*/
if ((errcode & 2) && !(pte_flags(gpte) & _PAGE_RW))
return false;
/* User access to a kernel-only page? (bit 3 == user access) */
if ((errcode & 4) && !(pte_flags(gpte) & _PAGE_USER))
return false;
/*
* Check that the Guest PTE flags are OK, and the page number is below
* the pfn_limit (ie. not mapping the Launcher binary).
*/
check_gpte(cpu, gpte);
/* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */
gpte = pte_mkyoung(gpte);
if (errcode & 2)
gpte = pte_mkdirty(gpte);
/* Get the pointer to the shadow PTE entry we're going to set. */
spte = spte_addr(cpu, *spgd, vaddr);
/*
* If there was a valid shadow PTE entry here before, we release it.
* This can happen with a write to a previously read-only entry.
*/
release_pte(*spte);
/*
* If this is a write, we insist that the Guest page is writable (the
* final arg to gpte_to_spte()).
*/
if (pte_dirty(gpte))
*spte = gpte_to_spte(cpu, gpte, 1);
else
/*
* If this is a read, don't set the "writable" bit in the page
* table entry, even if the Guest says it's writable. That way
* we will come back here when a write does actually occur, so
* we can update the Guest's _PAGE_DIRTY flag.
*/
set_pte(spte, gpte_to_spte(cpu, pte_wrprotect(gpte), 0));
/*
* Finally, we write the Guest PTE entry back: we've set the
* _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags.
*/
if (likely(!cpu->linear_pages))
lgwrite(cpu, gpte_ptr, pte_t, gpte);
/*
* The fault is fixed, the page table is populated, the mapping
* manipulated, the result returned and the code complete. A small
* delay and a trace of alliteration are the only indications the Guest
* has that a page fault occurred at all.
*/
return true;
}
/*H:330
* (i) Looking up a page table entry when the Guest faults.
*
* We saw this call in run_guest(): when we see a page fault in the Guest, we
* come here. That's because we only set up the shadow page tables lazily as
* they're needed, so we get page faults all the time and quietly fix them up
* and return to the Guest without it knowing.
*
* If we fixed up the fault (ie. we mapped the address), this routine returns
* true. Otherwise, it was a real fault and we need to tell the Guest.
*
* There's a corner case: they're trying to access memory between
* pfn_limit and device_limit, which is I/O memory. In this case, we
* return false and set @iomem to the physical address, so the the
* Launcher can handle the instruction manually.
*/
bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode,
unsigned long *iomem)
{
unsigned long gpte_ptr;
pte_t gpte;
pte_t *spte;
pmd_t gpmd;
pgd_t gpgd;
*iomem = 0;
/* We never demand page the Switcher, so trying is a mistake. */
if (vaddr >= switcher_addr)
return false;
/* First step: get the top-level Guest page table entry. */
if (unlikely(cpu->linear_pages)) {
/* Faking up a linear mapping. */
gpgd = __pgd(CHECK_GPGD_MASK);
} else {
gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
/* Toplevel not present? We can't map it in. */
if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
return false;
/*
* This kills the Guest if it has weird flags or tries to
* refer to a "physical" address outside the bounds.
*/
if (!check_gpgd(cpu, gpgd))
return false;
}
/* This "mid-level" entry is only used for non-linear, PAE mode. */
gpmd = __pmd(_PAGE_TABLE);
#ifdef CONFIG_X86_PAE
if (likely(!cpu->linear_pages)) {
gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
/* Middle level not present? We can't map it in. */
if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
return false;
/*
* This kills the Guest if it has weird flags or tries to
* refer to a "physical" address outside the bounds.
*/
if (!check_gpmd(cpu, gpmd))
return false;
}
/*
* OK, now we look at the lower level in the Guest page table: keep its
* address, because we might update it later.
*/
gpte_ptr = gpte_addr(cpu, gpmd, vaddr);
#else
/*
* OK, now we look at the lower level in the Guest page table: keep its
* address, because we might update it later.
*/
gpte_ptr = gpte_addr(cpu, gpgd, vaddr);
#endif
if (unlikely(cpu->linear_pages)) {
/* Linear? Make up a PTE which points to same page. */
gpte = __pte((vaddr & PAGE_MASK) | _PAGE_RW | _PAGE_PRESENT);
} else {
/* Read the actual PTE value. */
gpte = lgread(cpu, gpte_ptr, pte_t);
}
/* If this page isn't in the Guest page tables, we can't page it in. */
if (!(pte_flags(gpte) & _PAGE_PRESENT))
return false;
/*
* Check they're not trying to write to a page the Guest wants
* read-only (bit 2 of errcode == write).
*/
if ((errcode & 2) && !(pte_flags(gpte) & _PAGE_RW))
return false;
/* User access to a kernel-only page? (bit 3 == user access) */
if ((errcode & 4) && !(pte_flags(gpte) & _PAGE_USER))
return false;
/* If they're accessing io memory, we expect a fault. */
if (gpte_in_iomem(cpu, gpte)) {
*iomem = (pte_pfn(gpte) << PAGE_SHIFT) | (vaddr & ~PAGE_MASK);
return false;
}
/*
* Check that the Guest PTE flags are OK, and the page number is below
* the pfn_limit (ie. not mapping the Launcher binary).
*/
if (!check_gpte(cpu, gpte))
return false;
/* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */
gpte = pte_mkyoung(gpte);
if (errcode & 2)
gpte = pte_mkdirty(gpte);
/* Get the pointer to the shadow PTE entry we're going to set. */
spte = find_spte(cpu, vaddr, true, pgd_flags(gpgd), pmd_flags(gpmd));
if (!spte)
return false;
/*
* If there was a valid shadow PTE entry here before, we release it.
* This can happen with a write to a previously read-only entry.
*/
release_pte(*spte);
/*
* If this is a write, we insist that the Guest page is writable (the
* final arg to gpte_to_spte()).
*/
if (pte_dirty(gpte))
*spte = gpte_to_spte(cpu, gpte, 1);
else
/*
* If this is a read, don't set the "writable" bit in the page
* table entry, even if the Guest says it's writable. That way
* we will come back here when a write does actually occur, so
* we can update the Guest's _PAGE_DIRTY flag.
*/
set_pte(spte, gpte_to_spte(cpu, pte_wrprotect(gpte), 0));
/*
* Finally, we write the Guest PTE entry back: we've set the
* _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags.
*/
if (likely(!cpu->linear_pages))
lgwrite(cpu, gpte_ptr, pte_t, gpte);
/*
* The fault is fixed, the page table is populated, the mapping
* manipulated, the result returned and the code complete. A small
* delay and a trace of alliteration are the only indications the Guest
* has that a page fault occurred at all.
*/
return true;
}